Photographic techniques using silver halide have heretofore been most widely utilized, as the photographic characteristics thereof such as sensitivity, gradation control, etc., are superior to those of other photographic means such as electrophotography or diazo process. Recently, an improved photographic technique has been developed capable of simply and rapidly forming an image, where the image formation of a silver halide-containing photographic material is carried out by means of a process of heat development instead of a conventional wet process using a liquid developer at room temperature.
A photographic material for heat development is known in this technical field, and various photographic materials for heat development and processes thereof are described, for example, in Bases of Photographic Industry (by Corona Publishing, 1979), pp. 553 to 555; Film Information (April, 1978), p. 40; Neblette's Handbook of Photography and Reprography, 7th Ed. (Van Nostrand Reinhold Company), pp. 32-33; U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075; and British Patents Nos. 1,131,108 and 1,167,777; and Research Disclosure, RD No. 17029 (June, 1978), pp. 9-15.
Many processes have been proposed for formation of color images by heat development. As for means for formation of color images due to binding of a developing agent, as oxidized, and a coupler; U.S. Pat. No. 3,531,286 has proposed a combination of a p-phenylenediamine reducing agent and a phenolic or active methylene coupler; U.S. Pat. No. 3,761,270 describes a p-aminophenol reducing agent; Belgian Patent No. 802,519 and Research Disclosure, RD No. 137 (September, 1975), pp. 31-32 describe a sulfonamidophenol reducing agent; and U.S. Pat. No. 4,021,240 has proposed a combination of a sulfonamidophenol reducing agent and a tetra-equivalent coupler.
Other means for formation of positive color images include a photographic silver dye bleaching process as described, for example, in Research Disclosure, RD No. 14433 (April, 1976), pp. 30-32 and ibid., RD No. 15227 (December, 1976), pp. 14-15 and U.S. Pat. No. 4,235,957.
In addition, European Patent Applications Nos. 76,492A and 79,056A and Japanese Patent Application (OPI) Nos. 28928/83 and 26008/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") disclose a method for formation of color images by heat development, using a compound essentially having a dye part and capable of releasing a movable dye corresponding to or reversely corresponding to the reduction reaction reducing exposed silver halide to silver at a high temperature.
Japanese Patent Application (OPI) Nos. 58543/83, 79247/83 and 168439/84 describe a method for transferring a movable dye which has been imagewise formed by heat development to an image receiving layer with heat as well as image receiving materials used therefor.
In said image formation method including a heating step, however, all photographic reagents which are necessary for the development of photographic materials must necessarily be preliminarily incorporated in the photographic materials, since it is impossible to obtain the necessary photographic reagents from a developer, etc., during the heat treatment.
If, however, said photographic reagents are incorporated in the photographic materials in an active state, these will react with some other components contained in the photographic materials during preservation before their intended use or will be decomposed due to heat or in the presence of oxygen, with the result that said photographic reagents do not display the desired characteristics thereof.
One method has been proposed for the purpose of solving said problem, where the active groups in the photographic reagents are blocked by certain groups to be converted into substantially inactive forms, and thus such so-called photographic reagent precursors are incorporated in the photographic materials.
In the case that dye is used as the useful photographic reagent, the functional groups of said dye, which have a great influence on the spectral absorption of the dye, are blocked, whereby the spectral absorption is shifted to the side of a short wavelength range or to the side of a long wavelength range, with the result that when the thus-shifted dyes are incorporated in a photographic emulsion layer containing a silver halide emulsion having a photosensitive spectral range which corresponds to said dye, no filtering effect occurs, and thus sensitivity decrease is prevented. This is one advantageous merit.
In the case that an antifogging agent or a development inhibitor is used as the useful photographic reagent, the functional groups thereof are blocked whereby the adsorption of said reagents to photographic silver halides as well the desensitization due to the formation of silver salts during preservation of the photographic materials may be prevented, and, at the same time, these photographic reagents are released with desired timing, with the result that the occurrence of fog may be reduced without deterioration of the sensitivity, the occurrence of fog due to exceeding development may be inhibited and the development may be stopped in the necessary period of time. This is another advantageous merit.
In the case that a developing agent, an auxiliary developing agent, or a fogging agent is used as the useful photographic reagent, the functional groups or the adsorbing groups are blocked, whereby various photographically inconvenient actions may be prevented, which will result from the formation of semiquinones or oxidized compounds by air oxidation during preservation, or the introduction of electrons into silver halides may be prevented and the occurrence of fogged nuclei during preservation may be prevented, with the result that the photographic materials may be stably processed from a practical viewpoint. This is still another advantageous merit.
In the case that a bleaching accelerator or a bleaching-fixing accelerator is used as the photographic reagent, the active groups thereof are blocked, whereby the reaction of said reagent with other components contained in the photographic material during preservation thereof may be prevented. In the actual treatment of the materials, the blocked groups are unblocked, and thus the incorporated accelerators may display the desired action thereof in the necessary period of time. This is still another advantageous merit.
Regarding the blocking technique for the photographic reagents as mentioned above, blocked conventional photographic materials have heretofore been known. For instance, various known techniques have heretofore been conventional, including utilization as a blocking group of an acyl group or a sulfonyl group, as described in Japanese Patent Publication No. 44805/72; utilization of a blocked group capable of releasing a photographic reagent by a so-called reverse Michael reaction, as described in Japanese Patent Publication Nos. 17369/79, 9696/80 and 34927/80; utilization of a blocked group capable of releasing a photographic reagent with the formation of a quinonemethide compound or an analogue thereof by intramolecular electron transfer, as described in Japanese Patent Publication No. 39727/79, Japanese Patent Application (OPI) Nos. 135944/82, 135945/82 and 136640/82; utilization of an intramolecular ring closure reaction, as described in Japanese Patent Application (OPI) No. 53330/80; or utilization of ring cleavage of a 5-membered or 6-membered ring, as described in Japanese Patent Application (OPI) Nos. 76541/82, 135949/82 and 179842/82.
However, all of these conventional techniques utilize hydrolysis or proton removal by the action of OH.sup.- in a wet development which is carried out at room temperature. Thus, no technique has yet been known which uses a precursor in a heat development treatment with an organic base.